Wireless communication system, pilot sequence allocation apparatus, pilot sequence allocating method used for the system and apparatus, and mobile station used in the method

ABSTRACT

The present invention provides a method for allocating a pilot sequence that can obtain effect of reducing interference by combining received pilot blocks when sequence such as the CAZAC sequence as a pilot sequence is used. In the present invention, the pilot sequences by the number of 2K are divided into K sets of {C —   1,  C —   2 }, {C —   3,  C —   4 }, . . . , {C_( 2 K−1), C —   2 K} and allocated a set of the pilot sequences to each of the cells # 1  to #K. For example, pilot sequences: {C —   1,  C —   2 } are allocated to pilot blocks (SB # 1, #2 ) of the cell # 1 , pilot sequences: {C —   3,  C —   4 } are allocated to pilot blocks (SB # 1, #2 ) of the cell # 2 , pilot sequences: {C —   5,  C —   6 } are allocated to pilot blocks (SB # 1, #2 ) of the cell # 3 , and pilot sequences {C —   7,  C —   8 } are allocated to two pilot blocks (SB # 1, #2 ) of the cell # 4.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wireless communication system, apilot sequence allocation apparatus and a method for allocating pilotsequence used for the system and the apparatus and a mobile station usedin the method, and more specifically to the allocation of pilot sequencein a single carrier transmission system used in a wireless accessingmethod.

2. Description of the Prior Art

As an uplink wireless accessing method in the wireless communicationsystem of the next generation, a single carrier transmission method iseffective (refer to, for example, a Non-Patent document 1, “PhysicalLayer Aspects for Evolved UTRA” (3GPP TR25.814 v1.2.2 (2006-3), Chapter9.1.). The configuration of a frame format used in the singe carriertransmission method proposed in the Non-Patent document 1 is shown inFIG. 19.

In FIG. 19, a data signal is supposed to be sent in six LB (Long Block)#1 to #6 in a sub frame and a pilot signal is supposed to be sent in twoSB (Short Block) #1, #2.

CP (Cyclic Prefix) is added to the first half of the LB #1 to #6 and SB#1, #2 for effectively executing equalization of frequency regions atthe receiving side. Addition of CP is to copy the latter portion of theblock to the first portion as shown in FIG. 20.

As a pilot signal used in an uplink wireless accessing in the mobilecommunication system of the next generation, the Zadoff-Chu sequence,which is one of CAZAC (Constant Amplitude Zero Auto-Correlation)sequences, (refer to, for example, a Non-Patent document 2, K. Fazel andS. Keiser, “Multi-Carrier and Spread Spectrum Systems” (John Willey andSons, 2003)) is currently drawing attention.

The Zadoff-Chu sequence is represented by the formula:C _(—) k(n)=exp[−(j2πk/N)(n(n+½)+qn)]  (1).In the formula (1), n=0, 1, . . . , N, and q is an arbitrary integer andN is a sequence length.

The CAZAC sequence is a sequence that has constant amplitude in bothregions of time and frequency and it has always Zero Auto-Correlationfor time shift that is other than the cyclic self-correlation value is0. As the CAZAC sequence has Constant amplitude in a time region, it cankeep PAPR (Peak to Average Power Ratio) low. As the CAZAC sequence alsohas Constant amplitude in a frequency region, it is a sequence suitablefor propagation path estimation in the frequency region. Here, a smallPAPR means that it can keep the power consumption low. This feature ispreferred in the mobile communication.

Further, as the “CAZAC sequence” has a complete self-correlatingcharacteristic, it is advantageous in being appropriate for detecting atime of a received signal and draws attention as the pilot sequenceappropriate for a single carrier transmission, which is an uplinkwireless accessing method in the wireless communication system of thenext generation.

In the cellular environment (wireless communication network with aservice area divided into a plurality of cells), the base stationreceives not only an uplink signal of the mobile station in the cellmanaged by the base station as an uplink received signal but also anuplink signal of the mobile station of the other cell (particularly,adjacent cell) (see FIG. 1). The mobile station receives not only adownlink signal from the base station of the cell managed by the basestation but also a downlink signal of the base station of the other cellas it receives the uplink signal. Here, communication from the mobilestation to the base station is called an uplink and communication fromthe base station to the mobile station is called a downlink. Theabove-mentioned cell can also be called a sector.

As the base station captures a pilot signal from the mobile station inthe cell managed by the base station in the uplink communication, thepilot signal sent from the mobile station of the other cell needs to bereduced sufficiently. Thus, it is desirable that a set of smallsequences of correlation values is allocated as the pilot sequence ofcells adjacent to each other. In the downlink communication, it is alsodesirable that a set of small sequences of correlation values isallocated as the pilot sequence of cells adjacent to each other for thesame reason for the uplink communication.

The correlation characteristic of the CAZAC sequence largely depends onthe sequence length. That is to say, if the sequence length includes aprime number or a big prime number, the correlate characteristic is verygood (correlation value is small). In contrast, if the sequence lengthis a combined number comprising only small prime numbers (for example,an exponent such as 2 or 3), the correlate characteristic greatlydegrades (a big value is included in the correlation value).

Specifically, if the sequence length of Zadoff-Chu sequence is a primenumber, the correlation value of arbitrary sequences is always kept 1/√N(N is a sequence length and the root is a prime number) (for example,refer to the Non-Patent document 2). If the sequence length: N=127, thecorrelation value is always kept 1/√127, and if the sequence length:N=128, the worst value (the maximal value) of the correlation value is1/√2.

Sequences whose correlation value is 1/√N are abundant by the number of(N-1). From the viewpoint of a correlation value, it is proposed thatthe CAZAC sequence whose sequence length is the same primary number andwhose parameter [parameter in the formula (1)] is different is allocatedto each cell as a pilot sequence. As a result of that allocation, thenumber of sequences are (N-1), thus, the same pilot sequence needs to bere-performed for each of the (N-1) cells. The (N-1) will be called asthe number of repeating of the pilot sequences below.

On the other hand, if the pilot sequence is sent in a plurality ofblocks (two SB #1, #2 in the frame format shown in FIG. 19) as in theframe format of an uplink wireless access considered in the wirelesscommunication system of the next generation (see FIG. 19) and if a pilotsequence is allocated for each cell as mentioned above (that is to say,if sent pilot sequence is common in a plurality of pilot blocks in aframe and the pilot sequences used in SB #1, #2 of the frame formatshown in FIG. 19 are the same), an interference pattern from the othercell are the same in each pilot block at the receiving side.

That causes a problem in that no effect of reduction of interference byother cells by combining (averaging) a plurality of pilot blocks can beobtained at the receiving side. This is because no effect of reductionof interference by other cells can be obtained; as the pilot sequencessent in a plurality of pilot blocks are the same, interference from theother cells are received in the same manner (interference pattern) inevery pilot block to combine (average) them (see FIG. 21).

If a pilot sequence common in a plurality of pilot blocks in a frame isused in a conventional W-CDMA (Wideband-Code Division Multiple Access)and the like, a sequence which is a random sequence multiplied for aframe called a scrambling code is sent. Thus, a pattern of the pilotsequence to be sent differs for each pilot block so that the effect ofreduction of interference by other cells can be obtained by combining(averaging) a plurality of pilot blocks at the receiving side.

In the abovementioned conventional uplink wireless accessing system, ifa sequence such as the abovementioned CAZAC sequence is used as a pilotsequence, it is limited that a scrambling code cannot be applied to.This is because that a unique characteristic is lost [for example, CAZACcharacteristic (a characteristic advantageous for receiving such asconstant amplitude in a time and frequency regions, and the cyclicalself-correlation value is always 0 except for the case where the timeshift is 0)], as a result of multiplying a sequence such as the CAZACsequence by a random sequence such as a scrambling code.

If a sequence such as the CAZAC sequence is used as a pilot sequence andonly a code is allocated for each cell, the problem in that the effectof reduction of interference cannot be obtained by combining (averaging)received pilot blocks in the abovementioned frame cannot be avoided.

The object of the present invention is to provide a wirelesscommunication system, a pilot sequence allocation apparatus and a methodfor allocating pilot sequence to be used in the apparatus and a mobilestation using the method that eliminates the abovementioned problems andcan obtain the effect of reduction of interference by combining receivedpilot blocks if a sequence such as the CAZAC sequence is used as a pilotsequence.

BRIEF SUMMARY OF THE INVENTION

The first wireless communication system of the present invention is awireless communication system including a plurality of cells, a pilotsequence allocation apparatus for allocating a pilot sequence used incommunication between a base station and a mobile station to each cell,and the mobile station, comprising:

central processing unit provided in the pilot sequence allocationapparatus, of allocating different pilot sequence to each of a pluralityof pilot blocks in a frame for one of the plurality of cells, and

central processing unit provided in the mobile station, of allocatingthe different pilot sequence to each of a plurality of pilot blocks in aframe for said base station.

The second wireless communication system of the present invention isthat at least one of a plurality of pilot sequences allocated to one ofthe plurality of cells is different from at least one of a plurality ofpilot sequences allocated to a different cell.

The third wireless communication system of the present invention is thatthe pilot sequence allocation-apparatus divides the pilot sequence intosets of the number of pilot blocks in the frame and allocates the set toeach of the plurality of cells.

The fourth wireless communication system of the present inventionincludes N (N is an integer of 2 or more) pilot blocks in the frame, and

wherein the pilot sequence allocation apparatus performs allocation ofthe pilot sequence so that the pilot sequence is reused by the number ofrepeating cells M (M is an integer of 2 or more) and the pilot sequencesto be allocated to j^(th) pilot block (j=1, 2, . . . , N) of the cell i(i=1, 2, . . . , M) are different for different cells.

The fifth wireless communication system of the present invention is thatthe pilot sequence allocation apparatus performs allocation of the pilotsequence so that a pilot sequence to be allocated to j^(th) pilot blockof the cell i and a pilot sequence to be allocated to j′^(th) pilotblock of the cell i (j′≠j) are different.

The sixth wireless communication system of the present invention is thatthe pilot sequence allocation apparatus makes a pilot sequence allocatedto the j^(th) pilot block of the cell i a candidate for the sequence tobe allocated to j′^(th) (j′≠j) pilot block of the other cell i′ (i′≠i)again.

The seventh wireless communication system of the present invention isthat the pilot sequence allocation apparatus allocates the sequenceC_({i+j−2}) mod M}+1) to the j^(th) pilot block of the cell i so thatthe total number of the pilot sequence C_(1), C_(2), . . . , C_(M) isequal to the number of repeating cells M and the number of pilot blocksin one frame N is at the number of repeating cells M or less (N≦M).

The eighth wireless communication system of the present invention isthat the pilot sequence is the CAZAC (Constant Amplitude ZeroAuto-Correlation) sequence.

The ninth wireless communication system of the present invention is thata sequence length of the pilot sequence is a primary number length.

The first pilot sequence allocation apparatus of the present inventionis a pilot sequence allocation apparatus for allocating a pilot sequenceused in communication between a base station and a mobile station foreach of a plurality of cells of the wireless communication system,comprising:

central processing unit of allocating a pilot sequence different foreach of a plurality of pilot blocks in a frame for one of the pluralityof cells.

The second pilot sequence allocation apparatus of the present inventionis that at least one of a plurality of pilot sequences allocated to oneof the plurality of cells is different from at least one of a pluralityof pilot sequences allocated to a different cell.

The third pilot sequence allocation apparatus of the present inventionis that it divides the pilot sequence into sets of the number of pilotblocks in the frame and allocates the set to each of the plurality ofcells.

The fourth pilot sequence allocation apparatus of the present inventionallocates the pilot sequence so that the pilot sequence to be allocatedto the j^(th) pilot block (j=1, 2, . . . , N) of the cell i (i=1, 2, . .. , M) and a pilot sequence to be allocated to the j^(th) pilot block ofthe other cell are different from each other in a frame configurationincluding N (N is an integer of 2 or more) pilot blocks is included in aframe, when the pilot sequence is reused by the number of repeatingcells M (M is an integer of 2 or more).

The fifth pilot sequence allocation apparatus of the present inventionperforms allocation of the pilot sequence so that a pilot sequence to beallocated to j^(th) pilot block of the cell i and a pilot sequence to beallocated to j′^(th) pilot block of the cell i (j′≠j) are different.

The sixth pilot sequence allocation apparatus of the present inventionmakes a pilot sequence allocated to the j^(th) pilot block of the cell ia candidate for the sequence to be allocated to j′^(th) (j′≠j) pilotblock of the other cell i′ (i′≠i) again.

The seventh pilot sequence allocation apparatus of the present inventionallocates the sequence C_({i+j−2}) mod M}+1) to the j^(th) pilot blockof the cell i so that the total number of the pilot sequence C_(1),C_(2), . . . , C_(M) is equal to the number of repeating cells M and thenumber of pilot blocks in one frame N is at the number of repeatingcells M or less (N≦M).

The eighth pilot sequence allocation apparatus of the present inventionis that the pilot sequence is the CAZAC (Constant Amplitude ZeroAuto-Correlation) sequence.

The ninth pilot sequence allocation apparatus of the present inventionis that a sequence length of the pilot sequence is a primary numberlength.

The first method for allocating a pilot sequence of the presentinvention is a method for allocating a pilot sequence used in a wirelesscommunication system including a plurality of cells, a pilot sequenceallocation apparatus for allocating a pilot sequence used incommunication between a base station and a mobile station to each cell,and the mobile station, comprising in the pilot sequence allocationapparatus:

allocating different pilot sequence to each of a plurality of pilotblocks in a frame for one of said plurality of cells.

The second method for allocating a pilot sequence of the presentinvention is that at least one of a plurality of pilot sequencesallocated to one of the plurality of cells is different from at leastone of a plurality of pilot sequences allocated to a different cell.

The third method for allocating a pilot sequence of the presentinvention is that the pilot sequence allocation apparatus divides thepilot sequence into sets of the number of pilot blocks in the one frameand allocates the set to each of the plurality of cells.

The fourth method for allocating a pilot sequence of the presentinvention includes N (N is an integer of 2 or more) pilot blocks in theframe, and

wherein the pilot sequence allocation apparatus performs allocation ofthe pilot sequence so that the pilot sequence allocation apparatusreuses the pilot sequence by the number of repeating cells M (M is aninteger of 2 or more) and the pilot sequences to be allocated to j^(th)pilot block (j=1, 2, . . . , N) of the cell i (i=1, 2, . . . , M) aredifferent for different cells.

The fifth method for allocating a pilot sequence of the presentinvention is that the pilot sequence allocation apparatus performsallocation of the pilot sequence so that a pilot sequence to beallocated to j^(th) pilot block of the cell i and a pilot sequence to beallocated to j′^(th) pilot block the cell i (j′≠j) are different.

The sixth method for allocating a pilot sequence of the presentinvention is that the pilot sequence allocation apparatus makes a pilotsequence allocated to the j^(th) pilot block of the cell i a candidatefor the sequence to be allocated to j′^(th) (j′≠j) pilot block of theother cell i′ (i′≠i) again.

The seventh method for allocating a pilot sequence of the presentinvention is that the pilot sequence allocation apparatus allocates thesequence C_({i+j−2}) mod M}+1) to the j^(th) pilot block of the cell iso that the total number of the pilot sequence C_(1), C_(2), . . . ,C_(M) is equal to the number of repeating cells M and the number ofpilot blocks in the one frame N is at the number of repeating cells M orless (N≦M).

The eighth method for allocating a pilot sequence of the presentinvention is that the pilot sequence is the CAZAC (Constant AmplitudeZero Auto-Correlation) sequence.

The ninth method for allocating a pilot sequence of the presentinvention is that a sequence length of the pilot sequence is a primarynumber length.

The first mobile station of the present invention is a mobile stationfor communicating with a base station of a wireless communicationsystem, comprising:

central processing unit of sending a signal that allocates a differentpilot sequence to each of a plurality of pilot blocks in a frame for thebase station.

The second mobile station of the present invention is that the centralprocessing unit decides a pilot sequence to be allocated to theplurality of pilot blocks based on an index of the pilot sequencereceived from the base station.

The third mobile station of the present invention is at least one ofpilot sequences allocated to one of the plurality of pilot blocks isdifferent from at least one of a plurality of pilot sequences allocatedto the mobile station of a different cell.

The recording medium of the present invention is a recording medium thatrecords a program of a method for allocating a pilot sequence used in awireless communication system including a plurality of cells, a pilotsequence allocation apparatus for allocating a pilot sequence used incommunication between a base station and a mobile station to each cell,and the mobile station,

wherein the recording medium is provided in the pilot sequenceallocation apparatus and records a program for causing a computer toexecute allocating different pilot sequence to each of a plurality ofpilot blocks in a frame for the plurality of cells.

According to the present invention, significant effect of reduction ofinterference can be obtained by combining received pilot blocks when theabovementioned configurations and operations are used and a sequencesuch as the CAZAC sequence is used as a pilot sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of wirelesscommunication system by the first embodiment of the present invention;

FIG. 2 is a diagram showing a cell arrangement pattern used in the firstembodiment of the present invention;

FIG. 3 is a block diagram showing an example of a configuration of thepilot sequence allocation server of FIG. 1;

FIG. 4 is a diagram showing an example of a configuration of the mobilestations of FIG. 1;

FIG. 5 is a diagram showing a configuration of an allocationcorrespondence table showing a pilot sequence allocation by the firstembodiment of the present invention;

FIG. 6 is a diagram showing notification of a pilot sequence in thewireless communication system by the first embodiment of the presentinvention;

FIG. 7 is a diagram for illustrating effect of the pilot sequenceallocation in the wireless communication system by the first embodimentof the present invention;

FIG. 8 is a diagram showing a configuration of an allocationcorrespondence table showing an allocation of pilot sequence by thesecond embodiment of the present invention;

FIG. 9 is a diagram for illustrating effect of allocation of a pilotsequence in the wireless communication system by the second embodimentof the present invention;

FIG. 10 is a diagram showing a configuration of an allocationcorrespondence table showing allocation of pilot sequence by the thirdembodiment of the present invention;

FIG. 11 is a diagram showing a configuration of an allocationcorrespondence table showing allocation of pilot sequence by the fourthembodiment of the present invention;

FIG. 12 is a diagram showing a configuration of an allocationcorrespondence table showing allocation of pilot sequences by the fifthembodiment of the present invention;

FIG. 13 is a block diagram showing a system model of a simulationrelating to the present invention;

FIG. 14 is a diagram showing a simulation result in the presentinvention;

FIG. 15A to 15C are diagrams showing allocation examples of pilotsequence to the pilot blocks (SB #1, SB #2) used in simulation in thepresent invention;

FIG. 16A to 16C are diagrams showing allocation examples of pilotsequence to the pilot blocks (SB #1, SB #2) used in simulation in thepresent invention;

FIG. 17 is a diagram showing exemplary parameters used in a simulationrelating to the present invention;

FIG. 18 is a diagram showing a case where a data signal and a pilotsignal are multiplexed in a frequency region of a simulation in thepresent invention;

FIG. 19 is a diagram showing an example of a configuration of a frameformat used in the single carrier transmission method;

FIG. 20 is a diagram for illustrating addition of a cyclic prefix; and

FIG. 21 is a diagram for illustrating problems caused by conventionalallocation of pilot sequence.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, embodiments of the present invention will be described withreference to drawings.

Embodiment 1

FIG. 1 is a block diagram showing a configuration of wirelesscommunication system by the first embodiment of the present invention.In FIG. 1, the wireless communication system by the first embodiment ofthe present invention includes a pilot sequence allocation server 1,base stations (#1 to #3) 2-1 to 2-3, and mobile stations (#1 to #3) 3-1to 3-3.

At cells #1 to #3 managed by each of the base stations (#1 to #3) 2-1 to2-3, a signal of the pilot sequence allocated in a method to bedescribed below is sent as communication between the base stations (#1to #3) 2-1 to 2-3 and the mobile stations (#1 to #3) 3-1 to 3-3. Here,the communication from the mobile stations (#1 to #3) 3-1 to 3-3 to thebase stations (#1 to #3) 2-1 to 2-3 is called uplink communication andcommunication from the base stations to the mobile stations (#1 to #3)3-1 to 3-3 is called downlink communication.

A general wireless communication network with a service area dividedinto a plurality of cells #1 to #3 is supposed as a wirelesscommunication system by the first embodiment of the present invention.The plurality of base stations (#1 to #3) 2-1 to 2-3 are combinedtogether and connected to the pilot sequence allocation server 1. Thepilot sequence allocation server 1 needs not to be present independentof the base stations (#1 to #3) 2-1 to 2-3 and may be provided in any ofthe plurality of base stations (#1 to #3) 2-1 to 2-3. Further, the pilotsequence allocation server 1 may be provided in the higher-level deviceof the plurality of base stations (#1 to #3) 2-1 to 2-3 (for example, abase station controlling device or a core network) (not shown).

FIG. 2 is a diagram showing a cell arrangement pattern used in the firstembodiment of the present invention. FIG. 2 shows a seven cell repeatingpattern by seven base stations from #1 to #7. The pilot sequenceallocation server 1 allocates any of the seven indices from #1 to #7shown in FIG. 2 to each of the connected base stations. Based on theindices, the pilot sequence allocation server 1 performs pilot sequenceallocation to be described later for each of the seven base stationsthereunder.

A frame format to be used for sending communication data and a pilotsignal between the base stations (#1 to #3) 2-1 to 2-3 and the mobilestations (#1 to #3) 3-1 to 3-3 has a configuration as shown in FIG. 19.It is considered that a data signal is sent in six LBs (Long Block) #1to #6 by one sub-frame, and a pilot signal is sent in two SB (ShortBlock) #1, #2.

That is to say, in the embodiment, it is assumed that the number ofpilot blocks in one frame is two, the cell repetition factor in a pilotsequence is seven, and the pilot sequence used for sending is theZadoff-Chu sequence represented by the formula (1), and the number ofsequences used is seven, the same number as the cell repetition factor.The sequence is assumed as {C_1, C_2, C_3, C_4, C_5, C_6, C_7}.

Further, the pilot sequence allocation server 1 is assumed to previouslystore the cell repeating pattern of the base station (#1 to #3) 2-1 to2-3 each of which is connected to the server 1 (This means a cellarrangement pattern in which the same pilot patterns are not adjacent toeach other. In the embodiment, it is assumed the seven cell repeatingpattern as shown in FIG. 2).

FIG. 3 is a block diagram showing an example of a configuration of thepilot sequence allocation server 1 of FIG. 1. In FIG. 3, the pilotsequence allocation server 1 includes a CPU (central processing unit)11, a main memory 12 for storing a controlling program 12 a executed bythe CPU 11, a storage device 13 for storing data and the like used whenthe CPU 11 executes the controlling program 12 a and a communicationcontrolling device 14 for controlling communication with each of thebase stations (#1 to #3) 2-1 to 2-3.

The storage device 13 includes a cell repeating pattern storage area 131for storing the above-mentioned cell repeating pattern, a pilot sequencestorage area 132 for storing a pilot sequence, and an allocationcorrespondence storage area 133 storing an allocation correspondencetable showing correspondence between each of the base stations (cell #1to #K) and the pilot sequence to be allocated to the base station.

FIG. 4 is a block diagram showing an example of a configuration of themobile stations (#1 to #3) 3-1 to 3-3 of FIG. 1. In FIG. 4, the mobilestations 3 includes a CPU 31, a main memory 32 for storing a controllingprogram 32 a executed by the CPU 31, a storage device 33 for storingdata and the like used when the CPU 31 executes the controlling program32 a, and a communication controlling device 34 for controllingcommunication with each of the base stations (#1 to #3) 2-1 to 2-3. Themobile stations (#1 to #3) 3-1 to 3-3 have the same configuration asthat of the mobile station.

FIG. 5 is a diagram showing an allocation correspondence table showing apilot sequence allocation by the first embodiment of the presentinvention. FIG. 6 is a diagram showing notification of a pilot sequencein the wireless communication system by the first embodiment of thepresent invention. FIG. 7 is a diagram for illustrating effect of thepilot sequence allocation in the wireless communication system by thefirst embodiment of the present invention. Referencing to FIGS. 1 to 7,operations of the pilot sequence allocation in the wirelesscommunication system by the first embodiment of the present inventionwill be described.

The wireless communication system by the first embodiment of the presentinvention adopts a pilot sequence allocation method of dividing thepilot sequences by the number of 2K into K sets like {[C_1, C_2], [C_3,C_4], . . . , [C_(2K−1), C_2K]} and allocating a set of the pilotsequences to each of the cells #1 to #K (see FIG. 5).

That is to say, in FIG. 5, two pilot sequences: {C_1, C_2} are allocatedto two pilot blocks (SB #1, #2) of the cell #1, two pilot sequences:{C_3, C_4} are allocated to two pilot blocks (SB #1, #2) of the cell #2,two pilot sequences: {C_5, C_6} are allocated to two pilot blocks (SB#1, #2) of the cell #3, and two pilot sequences {C_7, C_8} are allocatedto two pilot blocks (SB #1, #2) of the cell #4.

Similarly, in FIG. 5, two pilot sequences {C_(2K−3), C_(2K−2)} areallocated to two pilot blocks (SB #1, #2) of the cell #(K−1), and twopilot sequences {C_(2K−1), C_2K} are allocated to two pilot blocks (SB#1, #2) of the cell #K.

As shown in FIG. 5, the pilot sequence allocation server 1 sends pilotsequence allocation information notification to each of the basestations (#1 to #3) 2-1 to 2-3 and allocates a pilot sequence to each ofthe base stations (#1 to #3) 2-1 to 2-3 based on the set allocationcorrespondence table. Each of the base stations (#1 to #3) 2-1 to 2-3notifies the mobile stations (#1 to #3) 3-1 to 3-3 by sending downlinknotification channel including an index of the allocated pilot sequenceor the like to a service area in the cells #1 to #3 [pilot sequencenotification to mobile station (#1 to #3) 3-1 to 3-3] (see FIG. 6).

Each of the mobile stations (#1 to #3) 3-1 to 3-3 in the service areaobtains an index of two pilot blocks (SB #1, #2) used in the cells (#1to #3) in which the self-station is present by receiving a downlinknotification channel or the like. Each of the mobile stations (#1 to #3)3-1 to 3-3 sends different pilot sequences for SB #1 and #2 based on theindex of the two pilot blocks obtained from the downlink notificationchannel or the like, when the mobile station sends data to each of thebase stations (#1 to #3) 2-1 to 2-3.

At this moment, an interference pattern that SB #1 receives from themobile station of another cell and an interference pattern that SB #2receives from the mobile station of another cell are different. That iseffective in reducing interference of another cell by combining(averaging) SB #1 and #2 in allocating a pilot sequence in theembodiment (see FIG. 7).

As such, in the embodiment, different pilot sequences can be sent indifferent pilot blocks in a frame (SB #1, #2) so that significant effectsuch as a plurality of receiving pilot blocks are combined (averaged)together at the receiving side to reduce an interference of another cellcan be obtained.

As mentioned above, as this embodiment is changed to allocate twosequences instead of a sequence to a cell in, the reused cell repetitionfactor of the pilot sequence is reduced. Each of the embodiments to bedescribed later devised on that point and also improves in that theamount of interference from a cell using the same code increases as adistance between the base stations using the same pilot sequencesdecreases. Although a method for allocating an uplink pilot sequence toeach cell has been described in the embodiment, the similar pilotsequence allocation method can be applied to the method for allocatingthe downlink pilot sequence to each cell.

Embodiment 2

FIG. 8 is a diagram showing an allocation correspondence table showingan allocation of pilot sequence by the second embodiment of the presentinvention. FIG. 9 is a diagram for illustrating effect of allocation ofa pilot sequence in the wireless communication system by the secondembodiment of the present invention.

The wireless communication system by the second embodiment of thepresent invention has the same configuration as that of the wirelesscommunication system by the first embodiment of the present inventionshown in FIG. 1 except for a method for allocating a pilot sequence. Thepilot sequence allocation server by the second embodiment of the presentinvention also has the same configuration as that of the pilot sequenceallocation server 1 by the first embodiment of the present inventionshown in FIG. 3. Further, the mobile station by the second embodiment ofthe present invention also has the same configuration as that of themobile station 3 by the first embodiment of the present invention shownin FIG. 4. The cell arrangement pattern used in the second embodiment ofthe present invention also has the same cell arrangement pattern used inthe first embodiment of the present invention shown in FIG. 2.

The pilot sequence allocation server 1 allocates one of the sevenindices from #1 to #7 shown in FIG. 2 to each of the connected basestations (#1 to #3) 2-1 to 2-3. Based on the indices, the pilot sequenceallocation server 1 allocates a pilot sequence for each of the sevenbase stations thereunder.

FIG. 8 shows an allocation correspondence table for allocating two pilotsequences: {C_K, C_(K+1)} (K=1, 2, . . . , 6) to each of the cells ofthe indices #K (K=1, 2, . . . , 7). In the case of K=7, {C_7, C_1} isallocated. The pilot sequence allocation server 1 sends pilot sequenceallocation information notification to each of the base stations (#1 to#3) 2-1 to 2-3 and allocates a pilot sequence to each of the basestations (#1 to #3) 2-1 to 2-3 based on the allocation correspondencetable set as shown in FIG. 8.

Each of the base stations (#1 to #3) 2-1 to 2-3 notices the mobilestations (#1 to #3) 3-1 to 3-3 by sending a downlink notificationchannel or the like including an index of the allocated pilot sequencesto the service area of the self-station [pilot sequence notification tomobile stations (#1 to #3) 3-1 to 3-3]. The mobile stations (#1 to #3)3-1 to 3-3 in the service area obtain an index of two pilot blocks (SB#1, #2) used in a cell in which the self-station is present by receivingthe downlink notification channel or the like. Then, the mobile stations(#1 to #3) 3-1 to 3-3 sends pilot sequences that are different for SB #1and #2 as shown in FIG. 9 based on the index of two pilot blocksobtained from the downlink notification channels and the like when itsends data to the base stations (#1 to #3) 2-1 to 2-3.

That is to say, in FIG. 8, two pilot sequences: {C_1, C_2} are allocatedto two pilot blocks (SB #1, #2) of the cell #1, two pilot sequences:{C_2, C_3} are allocated to two pilot blocks (SB #1, #2) of the cell #2,two pilot sequences: {C_3, C_4} are allocated to two pilot blocks (SB#1, #2) of the cell #3, and two pilot sequences {C_4, C_5} are allocatedto two pilot blocks (SB #1, #2) of the cell #4.

Similarly, in FIG. 8, two pilot sequences {C_(K−1), C_K} are allocatedto two pilot blocks (SB #1, #2) of the cell #(K−1), and two pilotsequences {C_K, C_1} are allocated to two pilot blocks (SB #1, #2) ofthe cell #K.

As such, in the embodiment, different pilot sequences can be sent indifferent pilot blocks (SB #1, #2) in a frame without decreasing thecell repetition factor for reusing a pilot sequence by allocating thepilot sequence allocated to SB #2 of a certain base station (cell) to SB#1 of the other base station (cell) again. From that, significant effectin reducing interference of another cell can be realized withoutdecreasing the cell repetition factor for reusing pilot sequences bycombining (averaging) a plurality of pilot blocks at the receiving sidein the embodiment.

Embodiment 3

FIG. 10 is a diagram showing an allocation correspondence table showingallocation of pilot sequence by the third embodiment of the presentinvention. The wireless communication system by the third embodiment ofthe present invention has the same configuration as that of the wirelesscommunication system by the first embodiment of the present inventionshown in FIG. 1 except for a method for allocating a pilot sequence. Thepilot sequence allocation server by the third embodiment of the presentinvention also has the same configuration as that of the pilot sequenceallocation server 1 by the first embodiment of the present inventionshown in FIG. 3. Further, the mobile station by the third embodiment ofthe present invention also has the same configuration as that of themobile station 3 by the first embodiment of the present invention shownin FIG. 4. The cell arrangement pattern used in the third embodiment ofthe present invention also has the same cell arrangement pattern used inthe first embodiment of the present invention as shown in FIG. 2.

The pilot sequence allocation server 1 allocates one of the sevenindices from #1 to #7 shown in FIG. 2 to each of the connected basestations (#1 to #3) 2-1 to 2-3. Based on the indices, the pilot sequenceallocation server 1 allocates a pilot sequence for each of the sevenbase stations thereunder.

FIG. 10 shows an allocation correspondence table for dividing cells bythe number of K for performing pilot allocation into some regions(groups) and allocating a set of pilot sequences for each of the dividedregions. The pilot sequence allocation server 1 sends pilot sequenceallocation information notification to each of the base stations (#1 to#3) 2-1 to 2-3 and allocates a pilot sequence to each of the basestations (#1 to #3) 2-1 to 2-3 based on the allocation correspondencetable set as shown in FIG. 10.

Each of the base stations (#1 to #3) 2-1 to 2-3 notices the mobilestations (#1 to #3) 3-1 to 3-3 by sending a downlink notificationchannel or the like including an index of the allocated pilot sequencesto the service area of the self-station [pilot sequence notification tomobile stations (#1 to #3) 3-1 to 3-3]. The mobile stations (#1 to #3)3-1 to 3-3 in the service area obtain an index of two pilot blocks (SB#1, #2) used in a cell in which the self-station is present by receivingthe downlink notification channel or the like. Then, the mobile stations(#1 to #3) 3-1 to 3-3 sends pilot sequences that are different for SB #1and #2 based on the index of two pilot blocks obtained from the downlinknotification channels and the like when it sends data to the basestations (#1 to #3) 2-1 to 2-3.

That is to say, in FIG. 10, the cell #1 and the cell #2 belong to thefirst divided region, and two pilot sequences: {C_1, C_2} are allocatedto two cells #1 and #2. Two pilot sequences: {C_1, C_2} are allocated totwo pilot blocks (SB #1, #2) of the cell #1 in the order of C_1, C_2. Onthe other hand, two pilot sequences: {C_1, C_2} are allocated to twopilot blocks (SB #1, #2) of the cell #2 in the order of C_2, C_1.

The cell #3 and the cell #4 belong to the second divided region, and twopilot sequences: {C_3, C_4} are allocated to two cells #3 and #4. Twopilot sequences: {C_3, C_4} are allocated to two pilot blocks (SB #1,#2) of the cell #3 in the order of C_3, C_4. On the other hand, twopilot sequences: {C_3, C_4} are allocated to two pilot blocks (SB #1,#2) of the cell #4 in the order of C_4, C_3.

Similarly, the cell # (K−1) and the cell #K belong to the K/2 dividedregion, with two pilot sequence {C_(K−1), C_K} being allocated to twocells # (K−1) and the cell #K. Two pilot sequence: {C_(K−1), C_K} areallocated to two pilot blocks (SB #1, #2) of the cell # (K−1) in theorder of C_(K−1) and C_K. On the other hand, two pilot sequences{C_(K−1), C_K} are allocated to two pilot blocks (SB #1, #2) of the cell#K in the order of C_K, C_(K−1).

As such, in the embodiment, different pilot sequences can be sent indifferent pilot blocks in a frame (SB #1, #2) without decreasing thecell repetition factor for reusing a pilot sequences by allocating thepilot sequence allocated to SB #1 and SB #2 of a certain base station toeach of SB #2 and SB #1 of the other base station again. With that, inthe embodiment, significant effect in reducing interference of anothercell can be achieved without reducing the cell repetition factor forreusing a pilot sequence by combining (averaging) a plurality ofreceived pilot blocks at the receiving side.

Embodiment 4

FIG. 11 is a diagram showing an allocation correspondence table showingallocation of pilot sequence by the fourth embodiment of the presentinvention. The wireless communication system by the fourth embodiment ofthe present invention has the same configuration as that of the wirelesscommunication system in the first embodiment of the present inventionshown in FIG. 1 except for the number of pilot blocks in a frame. Thepilot sequence allocation server by the fourth embodiment of the presentinvention has the same configuration as that of the pilot sequenceallocation server 1 by the first embodiment of the present inventionshown in FIG. 3. Further, the mobile station by the fourth embodiment ofthe present invention has the same configuration as that of the mobilestation 3 by the first embodiment of the present invention shown in FIG.4. The cell arrangement pattern used in the fourth embodiment of thepresent invention has the same cell arrangement pattern used in thefirst embodiment of the present invention shown in FIG. 2. Further, amethod for allocating a pilot sequence by the fourth embodiment of thepresent invention is the same method for allocating a pilot sequence bythe second embodiment of the present invention shown in FIG. 8.

That is to say, in FIG. 11, three pilot sequences: {C_1, C_2, C_3} areallocated to three pilot blocks (SB #1, #2, #3) of the cell #1, andthree pilot sequences: {C_2, C_3, C_4} are allocated to three pilotblocks (SB #1, #2, #3) of the cell #2.

In FIG. 11, three pilot sequences: {C_3, C_4, C_5} are allocated tothree pilot blocks (SB #1, #2, #3) of the cell #3, and three pilotsequences {C_4, C_5, C_6} are allocated to three pilot blocks (SB #1,#2, #3) of the cell #4.

Similarly, in FIG. 11, three pilot sequences {C_(K−1), C_K, C_1} areallocated to three pilot blocks (SB #1, #2, #3) of the cell #(K−1), andthree pilot sequences {C_K, C_1, C_2} are allocated to three pilotblocks (SB #1, #2, #3) of the cell #K.

As such, in the embodiment, different pilot sequences can be sent indifferent pilot blocks (SB #1, #2, #3) in a frame without decreasing thecell repetition factor for reusing a pilot sequence by allocating thepilot sequence allocated to SB #2 and SB #3 of a certain base station toSB #1 and SB #2 of the other base station again. From that, in theembodiment significant effect in reducing interference of another cellcan be realized without decreasing the cell repetition factor forreusing pilot sequences by combining (averaging) a plurality of receivedpilot blocks at the receiving side in the embodiment.

Embodiment 5

FIG. 12 is a diagram showing an allocation correspondence table showingallocation of pilot sequences by the fifth embodiment of the presentinvention. The wireless communication system by the fifth embodiment ofthe present invention has the same configuration as that of the wirelesscommunication system by the first embodiment of the present inventionshown in FIG. 1 except for the number of pilot blocks in a frame. Thepilot sequence allocation server by the fifth embodiment of the presentinvention also has the same configuration as that of the pilot sequenceallocation server 1 by the first embodiment of the present inventionshown in FIG. 3. Further, the mobile station by the fifth embodiment ofthe present invention also has the same configuration as that of themobile station 3 by the first embodiment of the present invention shownin FIG. 4. The cell arrangement pattern used in the fifth embodiment ofthe present invention also has the same cell arrangement pattern used inthe first embodiment of the present invention as shown in FIG. 2.Further, a method for allocating a pilot sequence by the fifthembodiment of the present invention is the same method for allocating apilot sequence by the second embodiment of the present invention asshown in FIG. 8.

That is to say, in FIG. 12, four pilot sequences: {C_1, C_2, C_3, C_4}are allocated to four pilot blocks (SB #1, #2, #3, #4) of the cell #1,and four pilot sequences: {C_2, C_3, C_4, C_5} are allocated to fourpilot blocks (SB #1, #2, #3, #4) of the cell #2.

In FIG. 12, four pilot sequences: {C_3, C_4, C_5, C_6} are allocated tofour pilot blocks (SB #1, #2, #3, #4) of the cell #3, and four pilotsequences: {C_4, C_5, C_6, C_7} are allocated to four pilot blocks (SB#1, #2, #3, #4) of the cell #4.

Similarly, in FIG. 12, four pilot sequences: {C_(K−1), C_K, C_1, C_2}are allocated to four pilot blocks (SB #1, #2, #3, #4) of the cell#(K−1), and four pilot sequences: {C_K, C_1, C_2, C_3} are allocated tofour pilot blocks (SB #1, #2, #3, #4) of the cell #K.

As such, in the embodiment, different pilot sequences can be sent indifferent pilot blocks in a frame (SB #1, #2, #3, #4) without decreasingthe cell repetition factor for reusing pilot sequences by allocating thepilot sequence allocated to SB #2, SB #3 and SB #4 of a certain basestation to SB #1, SB #2 and SB #3 of another base station again. Fromthat, a significant effect in reducing interference of another cellwithout decreasing the cell repetition factor for reusing a pilotsequence by combining (averaging) a plurality of received pilot blocksat the receiving side in the embodiment.

FIG. 13 is a block diagram showing a system model of a simulationrelating to the present invention. FIG. 14 is a diagram showing asimulation result relating to the present invention. FIGS. 15A to 15Cand 16A to 16C are diagrams showing exemplary allocation of pilotsequences to a pilot blocks (SB #1, SB #2) used in a simulation relatingto the present invention. FIG. 17 is a diagram showing exemplaryparameters used in a simulation relating to the present invention. FIG.18 is a diagram showing a case where a data signal and a pilot signalare multiplexed in a frequency region of a simulation relating to thepresent invention. Effects of the present invention will be describedwith reference to FIGS. 13 to 18.

As shown in FIG. 13, the wireless communication system of a simulationrelating the present invention includes two cells of a self-cell A andother cell B. The self-cell A has a self-cell base station 2 and theself-cell user [mobile station (UE) 3 a]. The other cell B has the othercell user [mobile station (UE) 3 b]. The self-cell base station 2receives a signal from the self-cell user [mobile station (UE) 3 a], andalso receives a signal from the other cell user [mobile station (UE) 3b] as interference. Further, in the simulation relating to the presentinvention, a frame of communication between a base station and a mobilestation is assumed to have two pilot blocks SB #1 and SB #2.

FIG. 14 shows block error rate characteristics of a signal that theself-cell base station 2 receives from the self-cell user [mobilestation (UE) 3 a]. The dotted line shows a result of the case where thesame pilot sequence is used in SB #1 and SB #2 [FIG. 15A table #1]. Thesolid line shows a result of the case where different pilot sequencesare used for SB #1 and SB #2 [FIG. 15B table #2].

The simulation relating to the present invention uses Localized FDM fordata multiplexing method, and Distributed-FDM pilot [1] (9. 1. 1. 2. 2Uplink reference-signal structure) for a pilot multiplexing method. Itis set SRF (Symbol Repetition Factor) of the pilot=4. Further, aninterference user from another cell is set to a user, and the averageinterference power is set to −6 dB for the average power of theself-cell user, and a frame timing between the self-cell user and theother cell user (interference user) is assumed to be synchronized with.

Further, the pilot sequence uses a sequence described in theabovementioned formula (1) (“k” in the formula is a parameter), thepilot sequence allocation to each user and each SB (allocation ofparameter “k”) is shown in each of the tables #1 to #6 in FIG. 15A to15C and FIG. 16A to 16C. For reference, the case of multiplexing dataand pilot in a frequency region at this moment is shown in FIG. 18 andparameters used in the simulation are shown in FIG. 17.

As shown in FIG. 14, it is apparent that Eb/No required for meeting theblock error rate=10⁻¹ is improved by near 1 dB. It is apparent thatEb/No required for meeting the block error rate=3×10⁻² is improved by 2dB or more.

It is assumed that the table #2 shown in FIG. 15B shows theabovementioned pilot allocation of the second embodiment of the presentinvention but the pilot allocation of the third embodiment of thepresent invention, i.e., allocation in the table #3 shown in FIG. 15Cmay achieve the same effects. For the pilot allocation of the firstembodiment of the present invention [pilot sequence allocation such asthe table #4 shown in FIG. 16A], the same effects may be achieved.

As the tables #5 and #6 shown in FIG. 16B, 16C, an effect of reducingthe other cell interference can be achieved even if the pilot sequenceused in SB #1 is the same as that in the other cell, if the sequenceused in SB #2 is different. Similarly, the same effect as that mentionedabove can be achieved even if SB #2 uses the same sequence as theadjacent cell, if a sequence different from that of the adjacent cell isused in SB #1. That is to say, if at least one of the pilot sequencesallocated to the self-cell is different from at least one of the pilotsequence allocated to the other cell, the same effect can be achieved.This is true in the case where the number of SBs in a frame is three ormore.

In the present invention, the cases where the number of pilot blocks ina frame is two or four have been respectively described above. Thepresent invention, however, can be applied to the cases where the numberof pilot blocks is five or more as to the cases where the number ofblocks is two or four.

1. A wireless communication system, comprising: a base station; and amobile station that sends a pilot signal to the base station, wherein aframe used for sending the pilot signal includes a first pilot block anda second pilot block, and wherein a first Zadoff-Chu sequence allocatedto the first pilot block is different from a second Zadoff-Chu sequenceallocated to the second pilot block.
 2. A pilot sequence allocationapparatus for allocating a pilot sequence used in uplink communication,comprising: an allocation unit that allocates a first Zadoff-Chusequence to a first pilot block and allocates a second Zadoff-Chusequence to a second pilot block that is different from the firstZadoff-Chu sequence, wherein the first pilot block and the second pilotblock are included in a frame used for the uplink communication.
 3. Amethod for allocating a pilot sequence used in uplink communication, themethod comprising: allocating a first Zadoff-Chu sequence to a firstpilot block; allocating a second Zadoff-Chu sequence to a second pilotblock that is different from the first Zadoff-Chu sequence, wherein thefirst pilot block and the second pilot block are included in a frameused for the uplink communication.
 4. A mobile station in a wirelesscommunication system including a base station, the mobile stationcomprising: a unit that sends a pilot signal to the base station,wherein a frame used for sending the pilot signal includes a first pilotblock and a second pilot block, and wherein a first Zadoff-Chu sequenceallocated to the first pilot block is different from a second Zadoff-Chusequence allocated to the second pilot block.
 5. A wirelesscommunication system including a base station and a mobile station, thesystem comprising: sending means provided in the mobile station, forsending a pilot signal to the base station, wherein a frame used forsending the pilot signal includes a first pilot block and a second pilotblock, and wherein a first Zadoff-Chu sequence allocated to the firstpilot block is different from a second Zadoff-Chu sequence allocated tothe second pilot block.
 6. A pilot sequence allocation apparatus forallocating a pilot sequence used in uplink communication, comprising:allocating means for allocating a first Zadoff-Chu sequence to a firstpilot block and allocating a second Zadoff-Chu sequence to a secondpilot block that is different from the first Zadoff-Chu sequence,wherein the first pilot block and the second pilot block are included ina frame used from the uplink communication.
 7. A mobile station in awireless communication system including a base station, the mobilestation comprising: sending means for sending a pilot signal to the basestation, wherein a frame used for sending the pilot signal includes afirst pilot block and a second pilot block, and wherein a firstZadoff-Chu sequence allocated to the first pilot block is different froma second Zadoff-Chu sequence allocated to the second pilot block.
 8. Amethod for a wireless communication system comprising a base station anda mobile station, the method comprising: sending a pilot signal to thebase station from the mobile station, wherein a frame used for sendingthe pilot signal includes a first pilot block and a second pilot block,and wherein a first Zadoff-Chu sequence allocated to the first pilotblock is different from a second Zadoff-Chu sequence allocated to thesecond pilot block.